Conventionally, apparatuses are known for continuously delivering a sheet from an original material roll formed by winding the sheet.
When a remaining sheet amount of the original material roll becomes small in an apparatus of this type, for example, a joining operation of sheets such as that shown in FIG. 29 to FIG. 32 is performed.
Specifically, in order to perform the joining operation, as shown in FIG. 29, adjacently to an original material roll (hereinafter, referred to as a delivery-side original material roll) R1 which delivers a sheet W, an original material roll (hereinafter, referred to as a standby-side original material roll) R2 which stands by for delivery of the sheet W is installed in advance.
As shown in FIG. 30, when a remaining amount of the sheet W of the delivery-side original material roll becomes small, an end section of the sheet W is retrieved from the standby-side original material roll R2 and an adhesive (for example, a tape T) is affixed to the end section of the sheet W.
Next, as shown in FIG. 31, using the tape T, the end section of the sheet W of the standby-side original material roll R2 is connected to an intermediate section of the sheet W of the delivery-side original material roll R1 and the sheet W of the delivery-side original material roll R1 is cut at an upstream position (a position denoted by a triangle in FIG. 31) relative to the tape T.
Accordingly, as shown in FIG. 32, tension applied to the sheet W on a downstream side of both original material rolls R1 and R2 is applied via the tape T to the sheet W of the standby-side original material roll R2, and the sheet W is delivered from the standby-side original material roll R2. In other words, the standby-side original material roll R2 performs a role of a next delivery-side original material roll R1.
As an apparatus for automatically performing the joining operation described above, for example, an apparatus described in Japanese Unexamined Patent Publication No. H7-101602 is known.
The apparatus described in Japanese Unexamined Patent Publication No. H7-101602 includes: a roll holding unit which holds a delivery-side original material roll and a standby-side original material roll; a joining unit which joins a sheet of the standby-side original material roll to a sheet of the delivery-side original material roll; a sensor which detects an end section of the sheet of the standby-side original material roll; and an XY mobile robot which retrieves the end section of the sheet of the standby-side original material roll detected by the sensor and which guides the end section to the joining unit.
The sensor is arranged so as to oppose an outer peripheral surface of the standby-side original material roll and detects a mark provided on the end section of the sheet of the standby-side original material roll.
However, with the apparatus described in Japanese Unexamined Patent Publication No. H7-101602, a mark must be provided on the standby-side original material roll in advance in order to detect a position of the end section of the sheet of the standby-side original material roll.
In this case, since a mark is unrelated to an original purpose of the sheet, additional work is created in order to remove the mark or discard a portion of the sheet where the mark is formed after a joining operation of the sheet.
On the other hand, detecting a position of the end section of the sheet of the standby-side original material roll in a state where a mark is omitted requires detecting a boundary between two sheets which have a same color and which are formed of a same material and, consequently, there is a risk that detection accuracy of the end section of the sheet may decline.